I think that this could work very well or very badly. It theoretically could work very well in terms of TURD, but I believe that TARD situation are going to be a major downfall. A quick redistribution of total overall health pool could put your tank into a situation where the next hit/special could kill them.
Let's put some numbers behind the situation:
4 group members have 100k health, while the tank has 200k (numbers are slightly skewed for more clarity and easier math). Your total base overall health pool is now 600k. Reading the tooltip, Sprit Totem will look at the current overall remaining group health and balance the entire group to end up with the same percentage of their individual maximum health pools. I am intentionally ignoring the 10% reduction as in my mind it's realitively a wash in this situation.
Tank takes massive damage during a bad RNG situation and drops to 75k health. All other health pools remain unaffected. Spirit Totme is popped and looks at available total group health, 475k, and balances it so that all group members end up with the same percent of health. So, 16.7%GMa + 16.7%GMb + 16.7%GMc + 16.6%GMd + 33.3%GMe(tank)=475k. So, health balances out to be 79.3kHPs for Group Memebers a, b, c, and d, and 158.3k for the tank. That's a very impressive redistribution heavily in favor of keeping the tank alive.
Tank is taking relatively little damage, but it is a highly TARD based fight. 2 of the 3 DPS and the Healer end up taking 75k damage each, with the other DPS moving out of the fire and only taking 25k damage. Tank is at 150k, while the healer is sitting also at 75k. So, 25k + 25k + 75k + 75k + 150k = 350k total group health pool. Spirit Totem is popped and redistribution happens resulting in Group Members a, b, c, and d with 58.5k each and 116.7k for the tank. Now, remember that each second, the health will be redistributed again. So your tank immediately takes a 30k hit from the boss, and 2 of your DPS take another 10k damage each. Your total health pool has been reduced by 50k and the redistribute hits. Now your group memebers end up with 50k each, and the tank at 100k. You cast Riptide, hit UE, resulting in 2 CGDs hoping to hit NS and GHW all the while, SLT is still redistributing health. How long before SLT drops the tank below Boss_Mob_damage?
I like the concept, but feel that redistribute every 1 second might be too much as we really can't get anything other than a NS GHW or Riptide off after that first pulse.
Let me know if my math is off by too much as it's only napkin.
Jornam 45 Jedi Sage - Sith Wyrm
85 Blood Tank / Frost DPS DK Kriscoe
85 Resto / Elemental Shaman Handalf